SAN BRUNO — Officials with this city say the California Public Utilities Commission is stonewalling them by refusing to hand over documents that the city suspects will show improper conduct at the PUC concerning deliberations over the fine it will assess PG&E for the deadly 2010 natural gas pipeline explosion in San Bruno.

City officials are seeking emails circulated among PUC Executive Director Paul Clanon and two administrative law judges, Mark Wetzell and Amy Yip-Kikugawa, who are preparing a proposed ruling on the fine. San Bruno wants to find out if Clanon pressured the judges to go easy on PG&E, which faces potential fines totaling $4 billion.

Britt Strottman, an Oakland attorney who represents San Bruno before the PUC, said other PUC employees familiar with the case have told city officials that Clanon urged the judges to drastically reduce PG&E’s potential fines by crediting the utility for upgrades it has made to its gas pipeline. Pressuring the judges would be highly improper, Strottman said, but added that only the emails will verify the actual nature of the communications.

“Until we can review the letters, we can’t assert anything about what they might or might not contain,” he said. “That’s why we want the emails. We don’t know what’s in there.”

San Bruno, which has been pushing for several months to get the records, suspects the PUC is refusing to hand them over because the discussions among the three officials could cast the PUC in a poor light at a time it is already under fire for failing to properly oversee PG&E. The decision on the fines for the San Bruno blast, which killed eight people and injured 58, is one of the most important and closely watched rulings the PUC has ever considered.

The PUC “could be embarrassed by the revelation of what is in the emails,” said Strottman.

In a letter to Strottman obtained by this newspaper, PUC staff counsel Fred Harris acknowledged that the PUC executive director and the administrative law judges in the San Bruno penalty case exchanged emails. But Harris refused to turn them over, arguing that they were “privileged” communications because they are part of an ongoing legal proceeding.

Clanon and the agency’s public relations staff did not respond to requests for comment from this newspaper.

Michael Asimow, a professor at Stanford Law School and an expert in administrative law, said certain communications between the PUC’s executive director and the administrative law judges would be improper during their deliberations.

“If there were substantive discussions on the matter, that could be improper,” he said.

Steven Weissman, director of the energy program at UC Berkeley Law School and a former PUC administrative law judge, said it would be acceptable for the executive director and the administrative law judges to discuss “procedural and staffing issues,” but added that “it would be typical for the executive director to discuss these things with the chief ALJ (administrative law judge) rather than going directly to the judge on the case.”

What is less clear, Weissman said, is when it would be appropriate for those parties to conduct discussions that might influence a ruling in a proceeding.

“If the executive director wants to affect the outcome of a case, it ought to be in a very public way so that everyone remains accountable,” Weissman said.

The issue is complicated by the fact that the PUC simultaneously functions as a judicial, legislative and administrative body. But experts say that when it is in the middle of a proceeding, it should act more like a court, with discussions staying on the record so all parties involved have fair access to information.

“Once agencies like the PUC start doing judicial procedures, they ought to behave under judicial principles,” said Reuel Schiller, a professor at UC Hastings College of Law.

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